Method and apparatus for generating a reference signal sequence in a wireless communication system

ABSTRACT

The present invention relates to a method and apparatus for generating a reference signal sequence in a wireless communication system. User equipment receives a cell-specific sequence hopping parameter from a base station, receives, from the base station, a user equipment (UE)-specific sequence group hopping (SGH) parameter which is specific to said user equipment, and generates a reference signal sequence on the basis of a base sequence number of a base sequence, wherein the base sequence number is determined for each slot on the basis of the cell-specific sequence hopping parameter and of the use equipment-specific sequence group hopping parameter. Here, the determination of whether or not to apply sequence hopping to the base sequence number indicated by the user equipment-specific sequence group hopping parameter overrides that of whether or not to apply sequence hopping to the base sequence number indicated by the cell-specific sequence hopping parameter.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the National Phase of PCT/KR2011/003555 filed on May13, 2011, which claims priority under 35 U.S.C. 119(e) to U.S.Provisional Application No. 61/334,555 filed on May 13, 2010 and under35 U.S.C. 119(a) to Patent Application No. 10-2011-0045104 filed in theRepublic of Korea on May 13, 2011, all of which are hereby expresslyincorporated by reference into the present application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wireless communication and, moreparticularly, to a method and an apparatus for generating a referencesignal sequence in a wireless communication system.

2. Related Art

Multiple-input multiple-output (MIMO) technology can be used to improvethe efficiency of data transmission and reception using multipletransmission antennas and multiple reception antennas. MIMO technologymay include a space frequency block code (SFBC), a space time block code(STBC), a cyclic delay diversity (CDD), a frequency switched transmitdiversity (FSTD), a time switched transmit diversity (TSTD), a precodingvector switching (PVS), spatial multiplexing (SM) for implementingdiversity. An MIMO channel matrix according to the number of receptionantennas and the number of transmission antennas can be decomposed intoa number of independent channels. Each of the independent channels iscalled a layer or stream. The number of layers is called a rank.

In wireless communication systems, it is necessary to estimate an uplinkchannel or a downlink channel for the purpose of the transmission andreception of data, the acquisition of system synchronization, and thefeedback of channel information. In wireless communication systemenvironments, fading is generated because of multi-path time latency. Aprocess of restoring a transmit signal by compensating for thedistortion of the signal resulting from a sudden change in theenvironment due to such fading is referred to as channel estimation. Itis also necessary to measure the state of a channel for a cell to whicha user equipment belongs or other cells. To estimate a channel ormeasure the state of a channel, a reference signal (RS) which is knownto both a transmitter and a receiver can be used.

A subcarrier used to transmit the reference signal is referred to as areference signal subcarrier, and a subcarrier used to transmit data isreferred to as a data subcarrier. In an OFDM system, a method ofassigning the reference signal includes a method of assigning thereference signal to all the subcarriers and a method of assigning thereference signal between data subcarriers. The method of assigning thereference signal to all the subcarriers is performed using a signalincluding only the reference signal, such as a preamble signal, in orderto obtain the throughput of channel estimation. If this method is used,the performance of channel estimation can be improved as compared withthe method of assigning the reference signal between data subcarriersbecause the density of reference signals is in general high. However,since the amount of transmitted data is small in the method of assigningthe reference signal to all the subcarriers, the method of assigning thereference signal between data subcarriers is used in order to increasethe amount of transmitted data. If the method of assigning the referencesignal between data subcarriers is used, the performance of channelestimation can be deteriorated because the density of reference signalsis low. Accordingly, the reference signals should be properly arrangedin order to minimize such deterioration.

A receiver can estimate a channel by separating information about areference signal from a received signal because it knows the informationabout a reference signal and can accurately estimate data, transmittedby a transmit stage, by compensating for an estimated channel value.Assuming that the reference signal transmitted by the transmitter is p,channel information experienced by the reference signal duringtransmission is h, thermal noise occurring in the receiver is n, and thesignal received by the receiver is y, it can result in y=h·p+n. Here,since the receiver already knows the reference signal p, it can estimatea channel information value ĥ using Equation 1 in the case in which aLeast Square (LS) method is used.ĥ=y/p=h+n/p=h+{circumflex over (n)}  [Equation 1]

The accuracy of the channel estimation value ĥ estimated using thereference signal p is determined by the value {circumflex over (n)}. Toaccurately estimate the value h, the value {circumflex over (n)} mustconverge on 0. To this end, the influence of the value {circumflex over(n)} has to be minimized by estimating a channel using a large number ofreference signals. A variety of algorithms for a better channelestimation performance may exist.

In transmitting a reference signal, group hoping (GH) or sequencehopping (SH) may be applied to a reference signal sequence to minimizeinter-cell interference (ICI).

In a multi-user (MU)-multiple-input multiple-output (MIMO) environment,an orthogonal covering code (OCC) may be applied to guaranteeorthogonality between reference signals that a plurality of userequipments transmits. By applying the OCC, the enhancement of theorthogonality and throughput may be guaranteed. Meanwhile, a pluralityof user equipments may use different bandwidths in the MU-MIMOenvironment. If the OCC is applied together while performing sequencehopping on reference signals that the plurality of user equipments withdifferent bandwidths transmits, the complexity of cell planningincreases. In other words, it is difficult to guarantee theorthogonality between the reference signals that the plurality of userequipments transmits.

Accordingly, another scheme is required to indicate whether to performsequence hopping on a reference signal sequence.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for generating areference signal sequence in a wireless communication system.

In an aspect, a method of generating a reference signal sequence by auser equipment (UE) in a wireless communication system is provided. Themethod includes receiving a cell-specific sequence hopping parameterfrom a base station, receiving a UE-specific sequence group hopping(SGH) parameter that is specific to the UE, from the base station, andgenerating a reference signal sequence based on a base sequence numberof a base sequence determined on a unit of each slot according to thecell-specific sequence hopping parameter and the UE-specific sequencegroup hopping parameter, wherein whether to apply a sequence hopping onthe base sequence number indicated by the UE-specific sequence grouphopping parameter overrides whether to apply the sequence hopping on thebase sequence number indicated by the cell-specific sequence hoppingparameter.

When that the sequence hopping is applied is indicated by thecell-specific sequence hopping parameter, and that the sequence hoppingis not applied is indicated by the UE-specific sequence group hoppingparameter, all the base sequence numbers of the base sequencesdetermined on the unit of each slot may be the same.

All the sequence numbers of the base sequences may be zeros.

A value of the cell-specific sequence hopping parameter may be 1, and avalue of the UE-specific sequence group hopping parameter may be 1.

The UE-specific sequence group hopping parameter may be transmittedthrough a higher layer.

The cell-specific sequence hopping parameter may be transmitted througha higher layer.

The base sequence number of the base sequence may be either 0 or 1.

The reference signal sequence may use physical uplink shared channel(PUSCH) resources and may be a demodulation reference signal (DMRS)sequence for demodulating a signal.

A length of the reference signal sequence may be larger than six times asize of a resource block (RB) in a frequency domain that is representedby a number of subcarriers.

The reference signal sequence may be generated by shifting the basesequence cyclically.

The method may further include receiving a cell-specific group hoppingparameter from the base station, and the cell-specific group hoppingparameter may indicate whether to apply a group hopping on a sequencegroup number of the base sequence determined on the unit of each slot.

That the group hoping to the sequence group number is not applied may beindicated by the cell-specific group hopping parameter.

The method may further includes mapping the reference signal sequence toa resource block that includes a plurality of subcarriers andtransmitting the result to the base station.

In another aspect, a user equipment (UE) for a wireless communicationsystem is provided. The UE includes a radio frequency (RF) unitconfigured for transmitting or receiving a radio signal, and a processorthat is connected to the RF unit, and configured for receiving acell-specific sequence hopping parameter from a base station, receivinga UE-specific sequence group hopping (SGH) parameter that is specific tothe UE, from the base station, and generating a reference signalsequence based on a base sequence number of a base sequence determinedon a unit of each slot according to the cell-specific sequence hoppingparameter and the UE-specific sequence group hopping parameter, whereinwhether to apply a sequence hopping on the base sequence numberindicated by the UE-specific sequence group hopping parameter overrideswhether to apply the sequence hopping on the base sequence numberindicated by the cell-specific sequence hopping parameter.

The invention may guarantee the orthogonality between a plurality ofuser equipments that use different bandwidths in an MU-MIMO environment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a wireless communication system.

FIG. 2 shows the structure of a radio frame in 3GPP LTE.

FIG. 3 shows an example of a resource grid of a single downlink slot.

FIG. 4 shows the structure of a downlink subframe.

FIG. 5 shows the structure of an uplink subframe.

FIG. 6 shows an example of the structure of a transmitter in an SC-FDMAsystem.

FIG. 7 shows an example of a scheme in which the subcarrier mapper mapsthe complex-valued symbols to the respective subcarriers of thefrequency domain.

FIG. 8 shows an example of the structure of a reference signaltransmitter for demodulation.

FIG. 9 shows examples of a subframe through which a reference signal istransmitted.

FIG. 10 shows an example of a transmitter using the clustered DFT-s OFDMtransmission scheme.

FIG. 11 shows another example of a transmitter using the clustered DFT-sOFDM transmission scheme.

FIG. 12 is another example of a transmitter using the clustered DFT-sOFDM transmission scheme.

FIG. 13 is an example where a plurality of UEs performs MU-MIMOtransmission using different bandwidths.

FIG. 14 shows an example where sequence hopping is not performed by auser equipment-specific SGH parameter according to an embodiment of thepresent invention.

FIG. 15 shows an example of a method of generating a reference signalsequence according to an embodiment of the present invention.

FIG. 16 is a block diagram illustrating a wireless communication systemwhere an embodiment of the present invention is implemented.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following technique may be used for various wireless communicationsystems such as code division multiple access (CDMA), a frequencydivision multiple access (FDMA), time division multiple access (TDMA),orthogonal frequency division multiple access (OFDMA), singlecarrier-frequency division multiple access (SC-FDMA), and the like. TheCDMA may be implemented as a radio technology such as universalterrestrial radio access (UTRA) or CDMA2000. The TDMA may be implementedas a radio technology such as a global system for mobile communications(GSM)/general packet radio service (GPRS)/enhanced data rates for GSMevolution (EDGE). The OFDMA may be implemented by a radio technologysuch as institute of electrical and electronics engineers (IEEE) 802.11(Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, E-UTRA (evolved UTRA), andthe like. IEEE 802.16m, an evolution of IEEE 802.16e, provides backwardcompatibility with a system based on IEEE 802.16e. The UTRA is part of auniversal mobile telecommunications system (UMTS). 3GPP (3rd generationpartnership project) LTE (long term evolution) is part of an evolvedUMTS (E-UMTS) using the E-UTRA, which employs the OFDMA in downlink andthe SC-FDMA in uplink. LTE-A (advanced) is an evolution of 3GPP LTE.

Hereinafter, for clarification, LTE-A will be largely described, but thetechnical concept of the present invention is not meant to be limitedthereto.

FIG. 1 shows a wireless communication system.

The wireless communication system 10 includes at least one base station(BS) 11. Respective BSs 11 provide a communication service to particulargeographical areas 15 a, 15 b, and 15 c (which are generally calledcells). Each cell may be divided into a plurality of areas (which arecalled sectors). A user equipment (UE) 12 may be fixed or mobile and maybe referred to by other names such as MS (mobile station), MT (mobileterminal), UT (user terminal), SS (subscriber station), wireless device,PDA (personal digital assistant), wireless modem, handheld device. TheBS 11 generally refers to a fixed station that communicates with the UE12 and may be called by other names such as eNB (evolved-NodeB), BTS(base transceiver system), access point (AP), etc.

In general, a UE belongs to one cell, and the cell to which a UE belongsis called a serving cell. A BS providing a communication service to theserving cell is called a serving BS. The wireless communication systemis a cellular system, so a different cell adjacent to the serving cellexists. The different cell adjacent to the serving cell is called aneighbor cell. A BS providing a communication service to the neighborcell is called a neighbor BS. The serving cell and the neighbor cell arerelatively determined based on a UE.

This technique can be used for downlink or uplink. In general, downlinkrefers to communication from the BS 11 to the UE 12, and uplink refersto communication from the UE 12 to the BS 11. In downlink, a transmittermay be part of the BS 11 and a receiver may be part of the UE 12. Inuplink, a transmitter may be part of the UE 12 and a receiver may bepart of the BS 11.

The wireless communication system may be any one of a multiple-inputmultiple-output (MIMO) system, a multiple-input single-output (MISO)system, a single-input single-output (SISO) system, and a single-inputmultiple-output (SIMO) system. The MIMO system uses a plurality oftransmission antennas and a plurality of reception antennas. The MISOsystem uses a plurality of transmission antennas and a single receptionantenna. The SISO system uses a single transmission antenna and a singlereception antenna. The SIMO system uses a single transmission antennaand a plurality of reception antennas. Hereinafter, a transmissionantenna refers to a physical or logical antenna used for transmitting asignal or a stream, and a reception antenna refers to a physical orlogical antenna used for receiving a signal or a stream.

FIG. 2 shows the structure of a radio frame in 3GPP LTE.

It may be referred to Paragraph 5 of “Technical Specification GroupRadio Access Network; Evolved Universal Terrestrial Radio Access(E-UTRA); Physical channels and modulation (Release 8)” to 3GPP (3rdgeneration partnership project) TS 36.211 V8.2.0 (2008 March). Referringto FIG. 2, the radio frame includes 10 subframes, and one subframeincludes two slots. The slots in the radio frame are numbered by #0 to#19. A time taken for transmitting one subframe is called a transmissiontime interval (TTI). The TTI may be a scheduling unit for a datatransmission. For example, a radio frame may have a length of 10 ms, asubframe may have a length of 1 ms, and a slot may have a length of 0.5ms.

One slot includes a plurality of orthogonal frequency divisionmultiplexing (OFDM) symbols in a time domain and a plurality ofsubcarriers in a frequency domain. Since 3GPP LTE uses OFDMA indownlink, the OFDM symbols are used to express a symbol period. The OFDMsymbols may be called by other names depending on a multiple-accessscheme. For example, when a single carrier frequency division multipleaccess (SC-FDMA) is in use as an uplink multi-access scheme, the OFDMsymbols may be called SC-FDMA symbols. A resource block (RB), a resourceallocation unit, includes a plurality of continuous subcarriers in aslot. The structure of the radio frame is merely an example. Namely, thenumber of subframes included in a radio frame, the number of slotsincluded in a subframe, or the number of OFDM symbols included in a slotmay vary.

3GPP LTE defines that one slot includes seven OFDM symbols in a normalcyclic prefix (CP) and one slot includes six OFDM symbols in an extendedCP.

The wireless communication system may be divided into a frequencydivision duplex (FDD) scheme and a time division duplex (TDD) scheme.According to the FDD scheme, an uplink transmission and a downlinktransmission are made at different frequency bands. According to the TDDscheme, an uplink transmission and a downlink transmission are madeduring different periods of time at the same frequency band. A channelresponse of the TDD scheme is substantially reciprocal. This means thata downlink channel response and an uplink channel response are almostthe same in a given frequency band. Thus, the TDD-based wirelesscommunication system is advantageous in that the downlink channelresponse can be obtained from the uplink channel response. In the TDDscheme, the entire frequency band is time-divided for uplink anddownlink transmissions, so a downlink transmission by the BS and anuplink transmission by the UE can be simultaneously performed. In a TDDsystem in which an uplink transmission and a downlink transmission arediscriminated in units of subframes, the uplink transmission and thedownlink transmission are performed in different subframes.

FIG. 3 shows an example of a resource grid of a single downlink slot.

A downlink slot includes a plurality of OFDM symbols in the time domainand N_(RB) number of resource blocks (RBs) in the frequency domain. TheN_(RB) number of resource blocks included in the downlink slot isdependent upon a downlink transmission bandwidth set in a cell. Forexample, in an LTE system, N_(RB) may be any one of 60 to 110. Oneresource block includes a plurality of subcarriers in the frequencydomain. An uplink slot may have the same structure as that of thedownlink slot.

Each element on the resource grid is called a resource element. Theresource elements on the resource grid can be discriminated by a pair ofindexes (k,l) in the slot. Here, k (k=0, . . . , N_(RB)×12−1) is asubcarrier index in the frequency domain, and l is an OFDM symbol indexin the time domain.

Here, it is illustrated that one resource block includes 7×12 resourceelements made up of seven OFDM symbols in the time domain and twelvesubcarriers in the frequency domain, but the number of OFDM symbols andthe number of subcarriers in the resource block are not limited thereto.The number of OFDM symbols and the number of subcarriers may varydepending on the length of a cyclic prefix (CP), frequency spacing, andthe like. For example, in case of a normal CP, the number of OFDMsymbols is 7, and in case of an extended CP, the number of OFDM symbolsis 6. One of 128, 256, 512, 1024, 1536, and 2048 may be selectively usedas the number of subcarriers in one OFDM symbol.

FIG. 4 shows the structure of a downlink subframe.

A downlink subframe includes two slots in the time domain, and each ofthe slots includes seven OFDM symbols in the normal CP. First three OFDMsymbols (maximum four OFDM symbols with respect to a 1.4 MHz bandwidth)of a first slot in the subframe corresponds to a control region to whichcontrol channels are allocated, and the other remaining OFDM symbolscorrespond to a data region to which a physical downlink shared channel(PDSCH) is allocated.

The PDCCH may carry a transmission format and a resource allocation of adownlink shared channel (DL-SCH), resource allocation information of anuplink shared channel (UL-SCH), paging information on a PCH, systeminformation on a DL-SCH, a resource allocation of an higher layercontrol message such as a random access response transmitted via aPDSCH, a set of transmission power control commands with respect toindividual UEs in a certain UE group, an activation of a voice overinternet protocol (VoIP), and the like. A plurality of PDCCHs may betransmitted in the control region, and a UE can monitor a plurality ofPDCCHs. The PDCCHs are transmitted on one or an aggregation of aplurality of consecutive control channel elements (CCE). The CCE is alogical allocation unit used to provide a coding rate according to thestate of a wireless channel. The CCE corresponds to a plurality ofresource element groups. The format of the PDCCH and an available numberof bits of the PDCCH are determined according to an associative relationbetween the number of the CCEs and a coding rate provided by the CCEs.

The BS determines a PDCCH format according to a DCI to be transmitted tothe UE, and attaches a cyclic redundancy check (CRC) to the DCI. Aunique radio network temporary identifier (RNTI) is masked on the CRCaccording to the owner or the purpose of the PDCCH. In case of a PDCCHfor a particular UE, a unique identifier, e.g., a cell-RNTI (C-RNTI), ofthe UE, may be masked on the CRC. Or, in case of a PDCCH for a pagingmessage, a paging indication identifier, e.g., a paging-RNTI (P-RNTI),may be masked on the CRC. In case of a PDCCH for a system informationblock (SIB), a system information identifier, e.g., a systeminformation-RNTI (SI-RNTI), may be masked on the CRC. In order toindicate a random access response, i.e., a response to a transmission ofa random access preamble of the UE, a random access-RNTI (RA-RNTI) maybe masked on the CRC.

FIG. 5 shows the structure of an uplink subframe.

An uplink subframe may be divided into a control region and a dataregion in the frequency domain. A physical uplink control channel(PUCCH) for transmitting uplink control information is allocated to thecontrol region. A physical uplink shared channel (PUCCH) fortransmitting data is allocated to the data region. If indicated by ahigher layer, the user equipment may support simultaneous transmissionof the PUCCH and the PUSCH.

The PUCCH for one UE is allocated in an RB pair. RBs belonging to the RBpair occupy different subcarriers in each of a 1^(st) slot and a 2^(nd)slot. A frequency occupied by the RBs belonging to the RB pair allocatedto the PUCCH changes at a slot boundary. This is called that the RB pairallocated to the PUCCH is frequency-hopped at a slot boundary. Since theUE transmits UL control information over time through differentsubcarriers, a frequency diversity gain can be obtained. In the figure,m is a location index indicating a logical frequency-domain location ofthe RB pair allocated to the PUCCH in the subframe.

Uplink control information transmitted on the PUCCH may include a HARQACK/NACK, a channel quality indicator (CQI) indicating the state of adownlink channel, a scheduling request (SR) which is an uplink radioresource allocation request, and the like.

The PUSCH is mapped to a uplink shared channel (UL-SCH), a transportchannel. Uplink data transmitted on the PUSCH may be a transport block,a data block for the UL-SCH transmitted during the TTI. The transportblock may be user information. Or, the uplink data may be multiplexeddata. The multiplexed data may be data obtained by multiplexing thetransport block for the UL-SCH and control information. For example,control information multiplexed to data may include a CQI, a precodingmatrix indicator (PMI), an HARQ, a rank indicator (RI), or the like. Orthe uplink data may include only control information.

FIG. 6 shows an example of the structure of a transmitter in an SC-FDMAsystem.

Referring to FIG. 6, the transmitter 50 includes a discrete Fouriertransform (DFT) unit 51, a subcarrier mapper 52, an inverse fast Fouriertransform (IFFT) unit 53, and a cyclic prefix (CP) insertion unit 54.The transmitter 50 may include a scramble unit (not shown), a modulationmapper (not shown), a layer mapper (not shown), and a layer permutator(not shown), which may be placed in front of the DFT unit 51.

The DFT unit 51 outputs complex-valued symbols by performing DFT oninput symbols. For example, when Ntx symbols are input (where Ntx is anatural number), a DFT size is Ntx. The DFT unit 51 may be called atransform precoder. The subcarrier mapper 52 maps the complex-valuedsymbols to the respective subcarriers of the frequency domain. Thecomplex-valued symbols may be mapped to resource elements correspondingto a resource block allocated for data transmission. The subcarriermapper 52 may be called a resource element mapper. The IFFT unit 53outputs a baseband signal for data (that is, a time domain signal) byperforming IFFT on the input symbols. The CP insertion unit 54 copiessome of the rear part of the baseband signal for data and inserts thecopied parts into the former part of the baseband signal for data.Orthogonality may be maintained even in a multi-path channel becauseinter-symbol interference (ISI) and inter-carrier interference (ICI) areprevented through CP insertion.

FIG. 7 shows an example of a scheme in which the subcarrier mapper mapsthe complex-valued symbols to the respective subcarriers of thefrequency domain. Referring to FIG. 7( a), the subcarrier mapper mapsthe complex-valued symbols, outputted from the DFT unit, to subcarrierscontiguous to each other in the frequency domain. ‘0’ is inserted intosubcarriers to which the complex-valued symbols are not mapped. This iscalled localized mapping. In a 3GPP LTE system, a localized mappingscheme is used. Referring to FIG. 7( b), the subcarrier mapper insertsan (L−1) number of ‘0’ every two contiguous complex-valued symbols whichare outputted from the DFT unit (L is a natural number). That is, thecomplex-valued symbols outputted from the DFT unit are mapped tosubcarriers distributed at equal intervals in the frequency domain. Thisis called distributed mapping. If the subcarrier mapper uses thelocalized mapping scheme as in FIG. 7( a) or the distributed mappingscheme as in FIG. 7( b), a single carrier characteristic is maintained.

FIG. 8 shows an example of the structure of a reference signaltransmitter for demodulation.

Referring to FIG. 8, the reference signal transmitter 60 includes asubcarrier mapper 61, an IFFT unit 62, and a CP insertion unit 63.Unlike the transmitter 50 of FIG. 6, in the reference signal transmitter60, a reference signal is directly generated in the frequency domainwithout passing through the DFT unit 51 and then mapped to subcarriersthrough the subcarrier mapper 61. Here, the subcarrier mapper may mapthe reference signal to the subcarriers using the localized mappingscheme of FIG. 7( a).

FIG. 9 shows examples of a subframe through which a reference signal istransmitted. The structure of a subframe in FIG. 9( a) shows a case of anormal CP. The subframe includes a first slot and a second slot. Each ofthe first slot and the second slot includes 7 OFDM symbols. The 14 OFDMsymbols within the subframe are assigned respective symbol indices 0 to13. Reference signals may be transmitted through the OFDM symbols havingthe symbol indices 3 and 10. The reference signals may be transmittedusing a sequence. A Zadoff-Chu (ZC) sequence may be used as thereference signal sequence. A variety of ZC sequences may be generatedaccording to a root index and a cyclic shift value. A BS may estimatethe channels of a plurality of UEs through an orthogonal sequence or aquasi-orthogonal sequence by allocating different cyclic shift values tothe UEs. The positions of the reference signals occupied in the twoslots within the subframe in the frequency domain may be identical witheach other or different from each other. In the two slots, the samereference signal sequence is used. Data may be transmitted through theremaining SC-FDMA symbols other than the SC-FDMA symbols through whichthe reference signals are transmitted. The structure of a subframe inFIG. 9( b) shows a case of an extended CP. The subframe includes a firstslot and a second slot. Each of the first slot and the second slotincludes 6 SC-FDMA symbols. The 12 SC-FDMA symbols within the subframeare assigned symbol indices 0 to 11. Reference signals are transmittedthrough the SC-FDMA symbols having the symbol indices 2 and 8. Data istransmitted through the remaining SC-FDMA symbols other than the SC-FDMAsymbols through which the reference signals are transmitted.

Although not shown in FIG. 9, a sounding reference signal (SRS) may betransmitted through the OFDM symbols within the subframe. The SRS is areference signal for UL scheduling which is transmitted from UE to a BS.The BS estimates a UL channel through the received SRS and uses theestimated UL channel in UL scheduling.

A clustered DFT-s OFDM transmission scheme is a modification of theexisting SC-FDMA transmission scheme and is a method of dividing datasymbols, subjected to a precoder, into a plurality of subblocks,separating the subblocks, and mapping the subblocks in the frequencydomain.

FIG. 10 shows an example of a transmitter using the clustered DFT-s OFDMtransmission scheme. Referring to FIG. 10, the transmitter 70 includes aDFT unit 71, a subcarrier mapper 72, an IFFT unit 73, and a CP insertionunit 74. The transmitter 70 may further include a scramble unit (notshown), a modulation mapper (not shown), a layer mapper (not shown), anda layer permutator (not shown), which may be placed in front of the DFTunit 71.

Complex-valued symbols outputted from the DFT unit 71 are divided into Nsubblocks (N is a natural number). The N subblocks may be represented bya subblock #1, a subblock #2, . . . , a subblock #N. The subcarriermapper 72 distributes the N subblocks in the frequency domain and mapsthe N subblocks to subcarriers. The NULL may be inserted every twocontiguous subblocks. The complex-valued symbols within one subblock maybe mapped to subcarriers contiguous to each other in the frequencydomain. That is, the localized mapping scheme may be used within onesubblock.

The transmitter 70 of FIG. 10 may be used both in a single carriertransmitter or a multi-carrier transmitter. If the transmitter 70 isused in the single carrier transmitter, all the N subblocks correspondto one carrier. If the transmitter 70 is used in the multi-carriertransmitter, each of the N subblocks may correspond to one carrier.Alternatively, even if the transmitter 70 is used in the multi-carriertransmitter, a plurality of subblocks of the N subblocks may correspondto one carrier. Meanwhile, in the transmitter 70 of FIG. 10, a timedomain signal is generated through one IFFT unit 73. Accordingly, inorder for the transmitter 70 of FIG. 10 to be used in a multi-carriertransmitter, subcarrier intervals between contiguous carriers in acontiguous carrier allocation situation must be aligned.

FIG. 11 shows another example of a transmitter using the clustered DFT-sOFDM transmission scheme. Referring to FIG. 11, the transmitter 80includes a DFT unit 81, a subcarrier mapper 82, a plurality of IFFTunits 83-1, 83-2, . . . , 83-N (N is a natural number), and a CPinsertion unit 84. The transmitter 80 may further include a scrambleunit (not shown), a modulation mapper (not shown), a layer mapper (notshown), and a layer permutator (not shown), which may be placed in frontof the DFT unit 71.

IFFT is individually performed on each of N subblocks. An n^(th) IFFTunit 38-n outputs an n^(th) baseband signal (n=1, 2, . . . , N) byperforming IFFT on a subblock #n. The n^(th) baseband signal ismultiplied by an n^(th) carrier signal to produce an n^(th) radiosignal. After the N radio signals generated from the N subblocks areadded, a CP is inserted by the CP insertion unit 314. The transmitter 80of FIG. 11 may be used in a discontiguous carrier allocation situationwhere carriers allocated to the transmitter are not contiguous to eachother.

FIG. 12 is another example of a transmitter using the clustered DFT-sOFDM transmission scheme. FIG. 12 is a chunk-specific DFT-s OFDM systemperforming DFT precoding on a chunk basis. This may be called NxSC-FDMA. Referring to FIG. 12, the transmitter 90 includes a code blockdivision unit 91, a chunk division unit 92, a plurality of channelcoding units 93-1, . . . , 93-N, a plurality of modulators 94-1, . . . ,4914-N, a plurality of DFT units 95-1, . . . , 95-N, a plurality ofsubcarrier mappers 96-1, . . . , 96-N, a plurality of IFFT units 97-1, .. . , 97-N, and a CP insertion unit 98. Here, N may be the number ofmultiple carriers used by a multi-carrier transmitter. Each of thechannel coding units 93-1, . . . , 93-N may include a scramble unit (notshown). The modulators 94-1, . . . , 94-N may also be called modulationmappers. The transmitter 90 may further include a layer mapper (notshown) and a layer permutator (not shown) which may be placed in frontof the DFT units 95-1, . . . , 95-N.

The code block division unit 91 divides a transmission block into aplurality of code blocks. The chunk division unit 92 divides the codeblocks into a plurality of chunks. Here, the code block may be datatransmitted by a multi-carrier transmitter, and the chunk may be a datapiece transmitted through one of multiple carriers. The transmitter 90performs DFT on a chunk basis. The transmitter 90 may be used in adiscontiguous carrier allocation situation or a contiguous carrierallocation situation.

A UL reference signal is described below.

In general, the reference signal is transmitted in the form of asequence. A specific sequence may be used as the reference signalsequence without a special limit. A phase shift keying (PSK)-basedcomputer generated sequence may be used as the reference signalsequence. Examples of PSK include binary phase shift keying (BPSK) andquadrature phase shift keying (QPSK). Alternatively, a constantamplitude zero auto-correlation (CAZAC) sequence may be used as thereference signal sequence. Examples of the CAZAC sequence include aZadoff-Chu (ZC)-based sequence, a ZC sequence with cyclic extension, anda ZC sequence with truncation. Alternatively, a pseudo-random (PN)sequence may be used as the reference signal sequence. Examples of thePN sequence include an m-sequence, a computer-generated sequence, a goldsequence, and a Kasami sequence. A cyclically shifted sequence may beused as the reference signal sequence.

A UL reference signal may be divided into a demodulation referencesignal (DMRS) and a sounding reference signal (SRS). The DMRS is areference signal used in channel estimation for the demodulation of areceived signal. The DMRS may be associated with the transmission of aPUSCH or PUCCH. The SRS is a reference signal transmitted from a UE to aBS for UL scheduling. The BS estimates an UL channel through thereceived SRS and uses the estimated UL channel in UL scheduling. The SRSis not associated with the transmission of a PUSCH or PUCCH. The samekind of a basic sequence may be used for the DMRS and the SRS.Meanwhile, in UL multi-antenna transmission, precoding applied to theDMRS may be the same as precoding applied to a PUSCH. Cyclic shiftseparation is a primary scheme for multiplexing the DMRS. In an LTE-Asystem, the SRS may not be precoded and may be an antenna-specificreference signal.

A reference signal sequence r_(u,v) ^((α))(n) may be defined based on abasic sequence b_(u,v)(n) and a cyclic shift a according to Equation 2.r _(u,v) ^((α))(n)=e ^(jαn) b _(u,v)(n), 0≦n<M _(sc) ^(RS)  [Equation 2]

In Equation 2, M_(sc) ^(RS)(1≦m≦N_(RB) ^(max,UL)) is the length of thereference signal sequence and M_(sc) ^(RS)=m*N_(sc) ^(RB). N_(sc) ^(RB)is the size of a resource block indicated by the number of subcarriersin the frequency domain. N_(RB) ^(max,UL) indicates a maximum value of aUL bandwidth indicated by a multiple of N_(sc) ^(RB). A plurality ofreference signal sequences may be defined by differently applying acyclic shift value a from one basic sequence.

A basic sequence b_(u,v)(n) is divided into a plurality of groups. Here,u□ {0, 1, . . . , 29} indicates a group index, and v indicates a basicsequence index within the group. The basic sequence depends on thelength M_(sc) ^(RS) of the basic sequence. Each group includes a basicsequence (v=0) having a length of M_(sc) ^(RS) for m (1≦m≦5) andincludes 2 basic sequences (v=0,1) having a length of M_(sc) ^(RS) for m(6≦m≦n_(RB) ^(max,UL)) The sequence group index u and the basic sequenceindex v within a group may vary according to time as in group hopping orsequence hopping.

Furthermore, if the length of the reference signal sequence is 3N_(sc)^(RB) or higher, the basic sequence may be defined by Equation 3.b _(u,v)(n)=x _(q)(n mod N _(ZC) ^(RS)), 0≦n<M _(sc) ^(RS)  [Equation 3]

In Equation 3, q indicates a root index of a Zadoff-Chu (ZC) sequence.N_(ZC) ^(RS) is the length of the ZC sequence and may be a maximum primenumber smaller than M_(sc) ^(RS). The ZC sequence having the root indexq may be defined by Equation 4.

$\begin{matrix}{{{x_{q}(m)} = {\mathbb{e}}^{{- j}\frac{\pi\;{{qm}{({m + 1})}}}{N_{ZC}^{RS}}}},{0 \leq m \leq {N_{ZC}^{RS} - 1}}} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack\end{matrix}$q may be given by Equation 5.q=└ q+ 1/2┘+v·(−1)^(└2 q┘)q=N _(ZC) ^(RS)·(u+1)/31  [Equation 5]

If the length of the reference signal sequence is 3N_(sc) ^(RB) or less,the basic sequence may be defined by Equation 6.b _(u,v)(n)=e ^(jφ(n)π/4), 0≦n≦M _(sc) ^(RS)−1  [Equation 6]

Table 1 is an example where φ(n) is defined when M_(sc) ^(RS)=N_(sc)^(RB).

TABLE 1 φ(0), . . . , φ(11) 0 −1 1 3 −3 3 3 1 1 3 1 −3 3 1 1 1 3 3 3 −11 −3 −3 1 −3 3 2 1 1 −3 −3 −3 −1 −3 −3 1 −3 1 −1 3 −1 1 1 1 1 −1 −3 −3 1−3 3 −1 4 −1 3 1 −1 1 −1 −3 −1 1 −1 1 3 5 1 −3 3 −1 −1 1 1 −1 −1 3 −3 16 −1 3 −3 −3 −3 3 1 −1 3 3 −3 1 7 −3 −1 −1 −1 1 −3 3 −1 1 −3 3 1 8 1 −33 1 −1 −1 −1 1 1 3 −1 1 9 1 −3 −1 3 3 −1 −3 1 1 1 1 1 10 −1 3 −1 1 1 −3−3 −1 −3 −3 3 −1 11 3 1 −1 −1 3 3 −3 1 3 1 3 3 12 1 −3 1 1 −3 1 1 1 −3−3 −3 1 13 3 3 −3 3 −3 1 1 3 −1 −3 3 3 14 −3 1 −1 −3 −1 3 1 3 3 3 −1 115 3 −1 1 −3 −1 −1 1 1 3 1 −1 −3 16 1 3 1 −1 1 3 3 3 −1 −1 3 −1 17 −3 11 3 −3 3 −3 −3 3 1 3 −1 18 −3 3 1 1 −3 1 −3 −3 −1 −1 1 −3 19 −1 3 1 3 1−1 −1 3 −3 −1 −3 −1 20 −1 −3 1 1 1 1 3 1 −1 1 −3 −1 21 −1 3 −1 1 −3 −3−3 −3 −3 1 −1 −3 22 1 1 −3 −3 −3 −3 −1 3 −3 1 −3 3 23 1 1 −1 −3 −1 −3 1−1 1 3 −1 1 24 1 1 3 1 3 3 −1 1 −1 −3 −3 1 25 1 −3 3 3 1 3 3 1 −3 −1 −13 26 1 3 −3 −3 3 −3 1 −1 −1 3 −1 −3 27 −3 −1 −3 −1 −3 3 1 −1 1 3 −3 −328 −1 3 −3 3 −1 3 3 −3 3 3 −1 −1 29 3 −3 −3 −1 −1 −3 −1 3 −3 3 1 −1

Table 2 is an example where φ(n) is defined when M_(sc) ^(RS)=2*N_(sc)^(RB).

TABLE 2 φ(0), . . . , φ(23) 0 −1 3 1 −3 3 −1 1 3 −3 3 1 3 −3 3 1 1 −1 13 −3 3 −3 −1 −3 1 −3 3 −3 −3 −3 1 −3 −3 3 −1 1 1 1 3 1 −1 3 −3 −3 1 3 11 −3 2 3 −1 3 3 1 1 −3 3 3 3 3 1 −1 3 −1 1 1 −1 −3 −1 −1 1 3 3 3 −1 −3 11 3 −3 1 1 −3 −1 −1 1 3 1 3 1 −1 3 1 1 −3 −1 −3 −1 4 −1 −1 −1 −3 −3 −1 11 3 3 −1 3 −1 1 −1 −3 1 −1 −3 −3 1 −3 −1 −1 5 −3 1 1 3 −1 1 3 1 −3 1 −31 1 −1 −1 3 −1 −3 3 −3 −3 −3 1 1 6 1 1 −1 −1 3 −3 −3 3 −3 1 −1 −1 1 −1 11 −1 −3 −1 1 −1 3 −1 −3 7 −3 3 3 −1 −1 −3 −1 3 1 3 1 3 1 1 −1 3 1 −1 1 3−3 −1 −1 1 8 −3 1 3 −3 1 −1 −3 3 −3 3 −1 −1 −1 −1 1 −3 −3 −3 1 −3 −3 −31 −3 9 1 1 −3 3 3 −1 −3 −1 3 −3 3 3 3 −1 1 1 −3 1 −1 1 1 −3 1 1 10 −1 1−3 −3 3 −1 3 −1 −1 −3 −3 −3 −1 −3 −3 1 −1 1 3 3 −1 1 −1 3 11 1 3 3 −3 −31 3 1 −1 −3 −3 −3 3 3 −3 3 3 −1 −3 3 −1 1 −3 1 12 1 3 3 1 1 1 −1 −1 1 −33 −1 1 1 −3 3 3 −1 −3 3 −3 −1 −3 −1 13 3 −1 −1 −1 −1 −3 −1 3 3 1 −1 1 33 3 −1 1 1 −3 1 3 −1 −3 3 14 −3 −3 3 1 3 1 −3 3 1 3 1 1 3 3 −1 −1 −3 1−3 −1 3 1 1 3 15 −1 −1 1 −3 1 3 −3 1 −1 −3 −1 3 1 3 1 −1 −3 −3 −1 −1 −3−3 −3 −1 16 −1 −3 3 −1 −1 −1 −1 1 1 −3 3 1 3 3 1 −1 1 −3 1 −3 1 1 −3 −117 1 3 −1 3 3 −1 −3 1 −1 −3 3 3 3 −1 1 1 3 −1 −3 −1 3 −1 −1 −1 18 1 1 11 1 −1 3 −1 −3 1 1 3 −3 1 −3 −1 1 1 −3 −3 3 1 1 −3 19 1 3 3 1 −1 −3 3 −13 3 3 −3 1 −1 1 −1 −3 −1 1 3 −1 3 −3 −3 20 −1 −3 3 −3 −3 −3 −1 −1 −3 −1−3 3 1 3 −3 −1 3 −1 1 −1 3 −3 1 −1 21 −3 −3 1 1 −1 1 −1 1 −1 3 1 −3 −1 1−1 1 −1 −1 3 3 −3 −1 1 −3 22 −3 −1 −3 3 1 −1 −3 −1 −3 −3 3 −3 3 −3 −1 13 1 −3 1 3 3 −1 −3 23 −1 −1 −1 −1 3 3 3 1 3 3 −3 1 3 −1 3 −1 3 3 −3 3 1−1 3 3 24 1 −1 3 3 −1 −3 3 −3 −1 −1 3 −1 3 −1 −1 1 1 1 1 −1 −1 −3 −1 325 1 −1 1 −1 3 −1 3 1 1 −1 −1 −3 1 1 −3 1 3 −3 1 1 −3 −3 −1 −1 26 −3 −11 3 1 1 −3 −1 −1 −3 3 −3 3 1 −3 3 −3 1 −1 1 −3 1 1 1 27 −1 −3 3 3 1 1 3−1 −3 −1 −1 −1 3 1 −3 −3 −1 3 −3 −1 −3 −1 −3 −1 28 −1 −3 −1 −1 1 −3 −1−1 1 −1 −3 1 1 −3 1 −3 −3 3 1 1 −1 3 −1 −1 29 1 1 −1 −1 −3 −1 3 −1 3 −11 3 1 −1 3 1 3 −3 −3 1 −1 −1 1 3

Hopping of a reference signal may be applied as follows.

The sequence group index u of a slot index n_(s) may be defined based ona group hopping pattern f_(gh)(n_(s)) and a sequence shift patternf_(ss) according to Equation 7.u(f _(gh)(n _(s))+f _(ss))mod 30  [Equation 7]

17 different group hopping patterns and 30 different sequence shiftpatterns may exist. Whether to apply group hopping may be indicated by ahigher layer.

A PUCCH and a PUSCH may have the same group hopping pattern. A grouphopping pattern f_(gh)(n_(s)) may be defined by Equation 8.

$\begin{matrix}{{f_{gh}\left( n_{s} \right)} = \left\{ \begin{matrix}0 & {{if}\mspace{14mu}{group}\mspace{14mu}{hopping}\mspace{14mu}{is}\mspace{14mu}{disabled}} \\{\left( {\sum\limits_{i = 0}^{7}\;{{c\left( {{8n_{s}} + i} \right)} \cdot 2^{i}}} \right){mod}\mspace{11mu} 30} & {{if}\mspace{14mu}{group}\mspace{14mu}{hopping}\mspace{14mu}{is}\mspace{14mu}{enabled}}\end{matrix} \right.} & \left\lbrack {{Equation}\mspace{14mu} 8} \right\rbrack\end{matrix}$

In Equation 8, c(i) is a pseudo random sequence that is a PN sequenceand may be defined by a Gold sequence of a length-31. Equation 9 showsan example of a gold sequence c(n).c(n)=(x ₁(n+N _(c))+x ₂(n+N _(c)))mod 2x ₁(n+31)=(x ₁(n+3)+x ₁(n))mod 2x ₂(n+31)=(x ₂(n+3)+x₂(n+2)+x ₁(n+1)+x ₁(n))mod 2  [Equation 9]

Here, Nc=1600, x₁(i) is a first m-sequence, and x₂(i) is a secondm-sequence. For example, the first m-sequence or the second m-sequencemay be initialized according to a cell identifier (ID) for every OFDMsymbol, a slot number within one radio frame, an OFDM symbol indexwithin a slot, and the type of a CP. A pseudo random sequence generatormay be initialized to

$c_{init} = \left\lfloor \frac{N_{ID}^{cell}}{30} \right\rfloor$in the first of each radio frame.

A PUCCH and a PUSCH may have the same sequence shift pattern. Thesequence shift pattern of the PUCCH may be f_(ss) ^(PUCCH)=N_(ID)^(cell) mod 30. The sequence shift pattern of the PUSCH may be f_(ss)^(PUCCH)=(f_(ss) ^(PUCCH)+Δ_(ss))mod 30 and Δ_(ss)ε{0, 1, . . . , 29}may be configured by a higher layer.

Sequence hopping may be applied to only a reference signal sequencehaving a length longer than 6N_(sc) ^(RB). Here, a basic sequence indexv within a basic sequence group of a slot index n_(s) may be defined byEquation 10.

$\begin{matrix}{v = \left\{ \begin{matrix}{c\left( n_{s} \right)} & \begin{matrix}{{if}\mspace{14mu}{group}\mspace{14mu}{hopping}\mspace{14mu}{is}\mspace{14mu}{disabled}\mspace{14mu}{and}} \\{{sequence}\mspace{14mu}{hopping}\mspace{14mu}{is}\mspace{14mu}{enabled}}\end{matrix} \\0 & {otherwise}\end{matrix} \right.} & \left\lbrack {{Equation}\mspace{14mu} 10} \right\rbrack\end{matrix}$c(i) may be represented by an example of Equation 9. Whether to applysequence hopping may be indicated by a higher layer. A pseudo randomsequence generator may be initialized to

$\begin{matrix}{c_{init} = {{\left\lfloor \frac{N_{ID}^{cell}}{30} \right\rfloor \cdot 2^{5}} + f_{ss}^{PUSCH}}} & \;\end{matrix}$in the first of each radio frame.

A DMRS sequence for a PUSCH may be defined by Equation 11.r ^(PUSCH)(m·M _(sc) ^(RS) +n)=r _(u,v) ^((α))(n)  [Equation 11]In Equation 11, m=0, 1, . . . and n=0, . . . , M_(sc) ^(RS)−1. M_(sc)^(RS)=M_(sc) ^(PUSCH).

α=2πn_(cs)/12, that is, a cyclic shift value is given within a slot, andn_(cs) may be defined by Equation 12.n _(cs)=(n _(DMRS) ⁽¹⁾ +n _(DMRS) ⁽²⁾ +n _(PRS)(n _(s)))mod12  [Equation 12]

In Equation 12, n_(DMRS) ⁽¹⁾ is indicated by a parameter transmitted bya higher layer, and Table 3 shows an example of a correspondingrelationship between the parameter and n_(DMRS) ⁽¹⁾.

TABLE 3 Parameter n_(DMRS) ⁽¹⁾ 0 0 1 2 2 3 3 4 4 6 5 8 6 9 7 10

Back in Equation 12, n_(DMRS) ⁽²⁾ may be defined by a cyclic shift fieldwithin a DCI format 0 for a transmission block corresponding to PUSCHtransmission. The DCI format is transmitted in a PDCCH. The cyclic shiftfield may have a length of 3 bits.

Table 4 shows an example of a corresponding relationship between thecyclic shift field and n_(DMRS) ⁽²⁾.

TABLE 4 Cyclic shift field in DCI format 0 n_(DMRS) ⁽²⁾ 000 0 001 6 0103 011 4 100 2 101 8 110 10 111 9

If a PDCCH including the DCI format 0 is not transmitted in the sametransmission block, if the first PUSCH is semi-persistently scheduled inthe same transmission block, or if the first PUSCH is scheduled by arandom access response grant in the same transmission block, n_(DMRS)⁽²⁾ may be 0.

n_(PRS)(n_(s)) may be defined by Equation 13.n _(PRS)(n _(s))=Σ_(i=0) ⁷ c(8N _(symb) ^(UL) ·n _(s)+i)·2^(i)  [Equation 13]c(i) may be represented by the example of Equation 9 and may be appliedin a cell-specific way of c(i). A pseudo random sequence generator maybe initialized to

$c_{init} = {{\left\lfloor \frac{N_{ID}^{cell}}{30} \right\rfloor \cdot 2^{5}} + f_{ss}^{PUSCH}}$in the first of each radio frame.

A DMRS sequence r^(PUSCH) is multiplied by an amplitude scaling factorβ_(PUSCH) and mapped to a physical transmission block, used in relevantPUSCH transmission, from r^(PUSCH)(0) in a sequence starting. The DMRSsequence is mapped to a fourth OFDM symbol (OFDM symbol index 3) in caseof a normal CP within one slot and mapped to a third OFDM symbol (OFDMsymbol index 2) within one slot in case of an extended CP.

An SRS sequence r_(SRS)(n)=r_(u,v) ^((α))(n) is defined. u indicates aPUCCH sequence group index, and v indicates a basic sequence index. Thecyclic shift value α is defined by Equation 14.

$\begin{matrix}{\alpha = {2\pi\frac{n_{SRS}^{cs}}{8}}} & \left\lbrack {{Equation}\mspace{14mu} 14} \right\rbrack\end{matrix}$

n_(SRS) ^(cs) is a value configured by a higher layer in related to eachUE and may be any one of integers from 0 to 7.

A proposed method of generating a reference signal sequence is describedbelow.

As described above, whether to perform a group hopping (GH) on areference signal sequence in LTE rel-8 may be indicated by a signal thatis transmitted in a cell-specific way. The cell-specific signalindicating whether to perform the group hopping on a reference signalsequence is hereinafter called a cell-specific GH parameter. AlthoughLTE rel-8 UE and LTE-A UE coexist within a cell, whether to perform thegroup hopping on a reference signal sequence is the same in the LTERel-8 UE and the LTE-A UE. Currently defined group hopping or a sequencehopping (SH) may be performed on a unit of each slot. The cell-specificGH parameter may be a Group-hopping-enabled parameter provided by ahigher layer. When the value of the Group-hopping-enabled parameter istrue, the group hopping for a reference signal sequence is performed,but the sequence hopping is not performed. When the value of theGroup-hopping-enabled parameter is false, the group hopping for areference signal sequence is not performed, and whether to perform thesequence hopping is determined by a cell-specific SH parameter, providedby a higher layer and indicating whether to perform the sequencehopping. The cell-specific SH parameter may be aSequence-hopping-enabled parameter provided by a higher layer.

Meanwhile, in the LTE-A, LTE rel-8 UE and LTE-A UE may perform MU-MIMOtransmission, or LTE-A UEs may perform MU-MIMO transmission. Here, inorder to support the MU-MIMO transmission of UEs having differentbandwidths, the OCC may be applied. When the OCC is applied,orthogonality between the UEs performing the MU-MIMO transmission can beimproved and the throughput can also be improved. However, if UEs havedifferent bandwidths and whether to perform the group hopping or thesequence hopping for a reference signal sequence is determined by acell-specific GH parameter or a cell-specific SH parameter defined inLTE rel-8, orthogonality between reference signals transmitted by therespective UEs may not be sufficiently guaranteed.

FIG. 13 is an example where a plurality of UEs performs MU-MIMOtransmission using different bandwidths. In FIG. 13( a), a first UE UE1and a second UE UE2 perform the same bandwidth. In this case, whether toperform the group hopping or the sequence hopping for a base sequence ofa reference signal may be determined by a cell-specific GH parameter ora cell-specific SH parameter defined in LTE rel-8. In FIG. 13( b), afirst UE UE1 uses a bandwidth which is the sum of bandwidths used by asecond UE UE2 and a third UE UE3. That is, the first UE, the second UE,and the third UE use different bandwidths. In this case, whether toperform the group hopping or the sequence hopping for a base sequence ofa reference signal transmitted by each UE needs to be determined using anew method.

Accordingly, a user equipment-specific sequence group hopping (SGH)parameter may be newly defined, which determines whether to performgroup hopping or sequence hopping on the base sequence of a referencesignal that each user equipment transmits. Hereinafter, a case isdescribed where whether to perform sequence hopping on the base sequenceof a reference signal is determined by the user equipment-specific SGHparameter. As the user equipment-specific SGH parameter is informationfor a specific user equipment, they may be transmitted only to thespecific user equipment. The user equipment-specific SGH parameters maybe applied to a DMRS that is transmitted using PUSCH resources assignedto a specific user equipment. In other words, the userequipment-specific SGH parameter may indicate whether to performsequence hopping on the base sequence of the DMRS transmitted using thePUSCH resources. For the convenience of description, it is defined thatwhether to perform sequence hopping on the base sequence of a referencesignal is determined only by the user equipment-specific SGH parameters,but the invention is not limited to this. Whether to perform sequencehopping on the base sequence of a reference signal may also bedetermined by the user equipment-specific SH parameter other than theuser equipment-specific SGH parameter. In addition, the inventiondescribes that it is applied to the base sequence of DMRS transmittedusing PUSCH resources, but the invention is not limited to this and mayalso be applied to DMRS, SRS, etc. that are transmitted using PUCCHresources. In addition, although the invention is based on an MU-MIMOenvironment where a plurality of user equipments has differentbandwidths, it may also be applied to an MU-MIMO environment where theuser equipments have the same bandwidth, or to a SU-MIMO environment.

When a value of the cell-specific GH parameter becomes false and grouphopping is not performed on the base sequence of a reference signal, avalue of the cell-specific SH parameter becomes true and sequencehopping may be performed on the base sequence of the reference signal.Then, sequence hopping in a slot level is performed on both DMRS thatuses PUSCH resources, and DMRS and SRS that use PUCCH resources, incommon. In other words, a base sequence index (or number) in a sequencegroup changes on a slot basis. Then, whether to perform sequence hoppingon DMRS that uses PUSCH resources may be indicated by the userequipment-specific SGH parameter. In other words, the userequipment-specific SGH parameter overrides the cell-specific SHparameter. The user equipment-specific SGH parameter may be a DisableSequence-group hopping parameter. In other words, if a value of the userequipment-specific SGH parameter becomes true, then sequence hopping isset not to be performed regardless of whether the value of thecell-specific SH parameter is true or false. More particularly, if theuser equipment-specific SGH parameter value is true, then sequencehopping on the base sequence of a reference signal is set not to beperformed even if an indication is made by the cell-specific SHparameter to perform sequence hopping on the base sequence of thereference signal. Since sequence hopping is not performed, the basesequence index of the base sequence of the reference signal does notchange on a slot basis. Then, since sequence hopping is not performedonly in one subframe, two slots in one subframe transmits the basesequence of the reference signal of the same base sequence index andsequence hopping may be applied between subframes. Alternatively, sincesequence hopping is not applied to the entire subframes, all slots mayalso transmit the base sequence of the reference signal of the same basesequence index. Meanwhile, when the user equipment-specific SGHparameter value is false, then sequence hopping on the base sequence ofa reference signal may be performed as indicated by the cell-specific SHparameter.

FIG. 14 shows an example where sequence hopping is not performed by auser equipment-specific SGH parameter according to an embodiment of thepresent invention. Referring to FIG. 14, when sequence hopping isperformed at LTE rel-8 or 9, the base sequence indices of the basesequences of reference signals transmitted from each slot are differentfrom one another. Then, the base sequence index of the base sequence ofa reference signal may be determined by Equation 10 previouslydescribed. If sequence hopping is not performed by a userequipment-specific SGH parameter, then zeros may be assigned to all thebase sequence indices of the base sequences of the reference signalstransmitted from each slot are all.

FIG. 15 shows an example of a method of generating a reference signalsequence according to an embodiment of the present invention.

At step S100, a user equipment receives a cell-specific SH parameterfrom a base station. At step S110, the user equipment receives a userequipment-specific SGH parameter from the base station. The userequipment-specific SGH parameter may be given by a higher layer. At stepS120, the user equipment generates a reference signal sequence based ona base sequence number of a base sequence determined on a slot basis.Then, whether to apply the sequence hopping of the base sequence numberindicated by the user equipment-specific SGH parameter overrides whetherto apply the sequence hopping of the base sequence number indicated bythe cell-specific SH parameter.

Whether to perform sequence hopping by the user equipment-specific SGHparameter may be known to a user equipment by various ways describedbelow.

-   1) A frequency hopping flag included in a DCI format for uplink    transmission may function as the user equipment-specific SGH    parameter. For example, if frequency hopping is enabled by the    frequency hopping flag, then sequence hopping may be performed in a    slot level. In addition, if frequency hopping is disabled by the    frequency hopping flag, sequence hopping may not be performed on the    base sequence of DMRS that uses PUSCH resources. Alternatively,    sequence hopping may be performed on a subframe basis.-   2) Whether to perform sequence hopping may be indicated by masking    information representing whether to perform SGH and SH on the base    sequence of a reference signal to a bit representing UE ID that is    included in the DCI format.-   3) When the specific index of a cyclic shift indicator included in    the DCI format for uplink transmission has been designated, whether    to perform sequence hopping on the base sequence of a reference    signal may be indicated.-   4) The DCI format for uplink transmission may include a user    equipment-specific SGH parameter that indicates whether to perform    the sequence hopping of the base sequence of the reference signal.-   5) The user equipment-specific SGH parameter may be transmitted to a    user equipment by higher layer signaling for a specific user    equipment.-   6) If a clustered DFT-s OFDM transmission scheme is used, then    sequence hopping may not be performed on the base sequence of the    reference signal.

Although it has been described above that whether to perform sequencehopping on the base sequence of the reference signal is determined bythe user equipment-specific SGH parameter, a parameter may be newlydefined, which indicates whether to further perform SH to furtherguarantee the orthogonality of the reference signals between userequipments in an MU-MIMO environment. The new parameter that indicateswhether to perform SH may be a user equipment-specific SH parameter. Theuser equipment-specific SH parameter may be applied in the same way asthe user equipment-specific SGH parameter previously described. In otherwords, the user equipment-specific SH parameter may override acell-specific SH parameter when being applied. Then, the userequipment-specific SGH parameter previously described may determine onlywhether to perform group hopping. In other words, when a value of theuser equipment-specific SGH parameter is true, then grouping hopping onthe base sequence of a reference signal is not performed. In addition,whether to perform sequence hopping on the base sequence of thereference signal is determined by the user equipment-specific SHparameter. If a value of the user equipment-specific SH parameter istrue, then sequence hopping is not performed on the base sequence of thereference signal. If a value of the user equipment-specific SH parameteris false, then whether to perform sequence hopping on the base sequenceof the reference signal may be determined by the cell-specific SHparameter. Dynamic signaling, such as signaling through PDCCH may begiven to the user equipment-specific SH parameter, implicitly orexplicitly. Alternatively, RRC signaling may be given to the parameterby a higher layer, implicitly or explicitly.

Meanwhile, although it is assumed in the description above that whenbeing applied, a user equipment-specific SGH parameter or a userequipment-specific SH parameter overrides a cell-specific SH parameterregardless of an uplink transmission mode, it may vary depending on atransmission mode. Single antenna transmission mode is basicallysupported in LTE rel-8/9, but a multiple antennal transmission mode, atransmission mode for supporting non-contiguous allocation, etc. may bedefined for efficiency of uplink transmission in LTE-A. When beingapplied, whether to override the user equipment-specific SGH parameteror the user equipment-specific SH parameter may be determined dependingon the transmission mode. For example, even if the userequipment-specific SGH parameter overrides the cell-specific SHparameter in single antenna transmission mode, whether to performsequence hopping on the base sequence of a reference signal may bedetermined by the cell-specific SH parameter, without considering that.

FIG. 16 is a block diagram illustrating a wireless communication systemwhere an embodiment of the present invention is implemented.

A base station 800 includes a processor 810, a memory 820, and a radiofrequency (RF) unit 830. The processor implements functions, processesand/or methods proposed. The layers of a wireless interface protocol maybe implemented by the processor 810. The memory 820 is connected to theprocessor 810 and stores various pieces of information for driving theprocessor 810. The RF unit 830 is connected to the processor 810, andtransmits/receives radio signals.

A user equipment 900 includes a processor 910, a memory 920, and an RFunit 930. The processor 910 implements functions, processes, and/ormethods proposed. The layers of a wireless interface protocol may beimplemented by the processor 910. The processor 910 is configured togenerate a reference signal sequence based on a base sequence on a slotbasis. The processor receives the cell-specific SH parameter from thebase station, receives the user equipment-specific SGH parameter thatare specific to the user equipments, from the base station, andgenerates a reference signal sequence based on a base sequence number ofa base sequence determined on a unit of each slot based on thecell-specific SH parameter and the user equipment-specific SGHparameter. At this point, whether to apply the sequence hopping of thebase sequence number indicated by the user equipment-specific SGHparameter overrides whether to apply the sequence hopping of the basesequence number indicated by the cell-specific SH parameters. The memory920 is connected to the processor 910 and stores various pieces ofinformation for driving the processor 910. The RF unit 930 is connectedto the processor 910, and transmits/receives radio signals.

The processors 810, 910 may include application-specific integratedcircuit (ASIC), other chipset, logic circuit and/or data processingdevice. The memories 820, 920 may include read-only memory (ROM), randomaccess memory (RAM), flash memory, memory card, storage medium and/orother storage device. The RF units 830, 930 may include basebandcircuitry to process radio frequency signals. When the embodiments areimplemented in software, the techniques described herein can beimplemented with modules (e.g., procedures, functions, and so on) thatperform the functions described herein. The modules can be stored inmemories 820, 920 and executed by processors 810, 910. The memories 820,920 can be implemented within the processors 810, 910 or external to theprocessors 810, 910 in which case those can be communicatively coupledto the processors 810, 910 via various means as is known in the art.

In view of the exemplary systems described herein, methodologies thatmay be implemented in accordance with the disclosed subject matter havebeen described with reference to several flow diagrams. While forpurposed of simplicity, the methodologies are shown and described as aseries of steps or blocks, it is to be understood and appreciated thatthe claimed subject matter is not limited by the order of the steps orblocks, as some steps may occur in different orders or concurrently withother steps from what is depicted and described herein. Moreover, oneskilled in the art would understand that the steps illustrated in theflow diagram are not exclusive and other steps may be included or one ormore of the steps in the example flow diagram may be deleted withoutaffecting the scope and spirit of the present disclosure.

What has been described above includes examples of the various aspects.It is, of course, not possible to describe every conceivable combinationof components or methodologies for purposes of describing the variousaspects, but one of ordinary skill in the art may recognize that manyfurther combinations and permutations are possible. Accordingly, thesubject specification is intended to embrace all such alternations,modifications and variations that fall within the spirit and scope ofthe appended claims.

What is claimed is:
 1. A method of generating a reference signalsequence by a user equipment (UE) in a wireless communication system,the method comprising: receiving a cell-specific group hopping parameterfrom a base station, wherein the cell-specific group hopping parameteris used to disable a group hopping for a plurality of UEs in a cell;receiving a cell-specific sequence hopping parameter from the basestation, wherein the cell-specific sequence hopping parameter is used toenable a sequence hopping for the plurality of UEs in the cell;receiving a UE-specific sequence group hopping (SGH) parameter,specified to the UE, from the base station, wherein the UE-specific SGHparameter is used to disable the sequence hopping, enabled by thecell-specific sequence hopping parameter, for the UE; and generating thereference signal sequence based on a base sequence number within a basesequence group, wherein the base sequence number within the basesequence group is determined by the UE-specific SGH parameter.
 2. Themethod of claim 1, wherein all the base sequence numbers within the basesequence group in each slot are the same.
 3. The method of claim 2,wherein all the base sequence numbers within the base sequence group ineach slot are zeros.
 4. The method of claim 1, wherein the UE-specificSGH parameter is received through a higher layer.
 5. The method of claim1, wherein the cell-specific sequence hopping parameter is receivedthrough a higher layer.
 6. The method of claim 1, wherein the basesequence number within the base sequence group in each slot is either 0or
 1. 7. The method of claim 1, wherein the reference signal sequenceuses physical uplink shared channel (PUSCH) resources and is ademodulation reference signal (DMRS) sequence for demodulating a signal.8. The method of claim 1, wherein a length of the reference signalsequence is larger than six times a size of a resource block (RB) in afrequency domain that is represented by a number of subcarriers.
 9. Themethod of claim 1, wherein the reference signal sequence is generated byshifting a base sequence cyclically.
 10. The method of claim 1, furthercomprising: mapping the reference signal sequence to a resource blockthat includes a plurality of subcarriers and transmitting the result tothe base station.
 11. A user equipment (UE) for a wireless communicationsystem, the UE comprising: a radio frequency (RF) unit configured totransmit or receive a radio signal; and a processor connected to the RFunit, and configured to: receive a cell-specific group hopping parameterfrom a base station, wherein the cell-specific group hopping parameteris used to disable a group hopping for a plurality of UEs in a cell,receive a cell-specific sequence hopping parameter from the basestation, wherein the cell-specific sequence hopping parameter is used toenable a sequence hopping for the plurality of UEs in the cell, receivea UE-specific sequence group hopping (SGH) parameter, specified to theUE, from the base station, wherein the UE-specific SGH parameter is usedto disable the sequence hopping, enabled by the cell-specific sequencehopping parameter, for the UE, and generate the reference signalsequence based on a base sequence number within a base sequence group,wherein the base sequence number within the base sequence group isdetermined by the UE-specific SGH parameter.